填空题 Try to picture a slow expansion of human activities outward from the solar system, among the suns in our galaxy. Imagine a vast ocean sprinkled with islands, some deserted, 1 perhaps inhabited. On one of the 2 islands, people have just learned how to build ships. They prepare to 3 the ocean, but the very nearest island is five years" voyaging 4 . No possible improvement in the technique of ship-building will ever reduce this time.
After a few centuries the islanders may have established colonies on many of the 5 islands and briefly explored others. Returning 6 from any of the colonies could report only 7 had happened there five years ago. There would never be news from the other islands— 8 history.
Beyond our own galaxy—the whirlpool of stars and cosmic dust 9 which our sun is an out-of-town member, lying on one of the remoter spiral arms—are other 10 . There are probably as many other galaxies in creation as there are 11 in our own.
The detailed examination of all the 12 of sand on all the beaches of the world is a minor exercise compared to the exploration of the universe. Space can be charted and crossed and occupied without definable limit, but it can never be 13 . When we have reached our ultimate achie vements in space and the stars themselves are scattered no more widely than mankind, even then we shall still be like ants 14 on the face of the earth. The ants have covered the world, but have they conquered 15 —for what do their countless colonies know of it, or of each other?